As the density of semiconductor devices, typified by DRAMs (Dynamic Random Access Memory) and the like, has increased, it has become desirable to form holes having a high aspect ratio (hereinafter referred to as high-aspect holes) in interlayer insulating films such as silicon dioxide films which form the semiconductor device.
If the layout of the DRAM cells allows cylinder holes for capacitors to have a close-packed arrangement, it is preferable for the planar shape of the cylinder holes to be circular, but if a close-packed arrangement is problematic, the planar shape is preferably elliptical.
However, high-aspect holes are formed by dry etching using a hardmask, and in order to obtain a required etching selectivity to cope with increasing aspect ratios, there is a tendency for hardmasks to be multi-layered. With such a multi-layered hardmask, an elliptical pattern is formed on the uppermost layer by photolithography, using a reticle provided with an elliptical pattern, but there is a problem in that when the pattern is then repeatedly process-transferred from an upper layer portion to a lower layer portion of the hardmask, the ellipticity (the ratio of the major diameter to the minor diameter) of the pattern gradually decreases as a result of a reduction in the processing accuracy, and when the hardmask is completed, the pattern is substantially circular, and it is not possible to form the required elliptical hole.
Meanwhile, Japanese Patent Kokai 2010-272714 (patent literature article 1) discloses a method of forming a capacitor using double-patterning in order prevent a deterioration in the accuracy of the pattern transfer attributable to the characteristics of lithography.
More specifically, patent literature article 1 discloses a method of forming a columnar capacitor using double-patterning, including: a step of forming an insulating film on a semiconductor substrate; a step of forming on the insulating film a first mask having a strip-shaped pattern extending in a first direction; a step of forming a strip-shaped body by processing the insulating film into a strip-shaped body by etching the insulating film using the first mask as a mask; a step of forming on the strip-shaped body a second mask having a strip-shaped pattern extending in a second direction that is different from the first direction; and a step of forming a columnar body by processing the strip-shaped body into a columnar body by etching the strip-shaped body using the second mask as a mask.
However, with columnar capacitors, capacitors can only be formed on the columnar side surfaces, and since the capacitance is therefore small, they cannot be employed in miniaturized semiconductor devices. Capacitors used in miniaturized semiconductor devices must therefore have a crown structure, in which the inner and outer surfaces of a lower electrode are used as capacitors. In this case, cylinder holes, on the inner surfaces of which lower electrodes are formed, must be formed in the insulating film. Further, it is desirable for the planar shape of the cylinder hole to be formed as an ellipse.